A conventional transmission for a powered vehicle can include a gearbox, i.e., gears, synchronizers, dog clutches, clutch plates and reaction plates, a number of automatically selectable gears, planetary gear sets, hubs, pistons, shafts, and other housings. The clutches can be stationary brakes/clutches or rotating clutches. The transmission can have an internal shaft which rotates one or more clutches or shafts in the transmission.
The number of clutches and gear schemes can be used to achieve different gear ratios. Each gear ratio can define a range in which the transmission operates. A higher numerical gear ratio, for example, can be achieved at a lower transmission output speed. This can be important if a vehicle is heavily loaded or requires higher torque to ascend an elevation, for instance. Alternatively, a lower numerical gear ratio can be achieved at a higher transmission output speed, particularly when a vehicle is travelling at higher speeds on a highway. The lower numerical gear ratio can help increase fuel efficiency at these speeds.
To achieve different gear ratios, gear schemes are configured in which brakes, clutches, shafts, and gearsets are packaged in a transmission. The gear scheme can include one or more planetary gearsets. A planetary gearset can include a sun gear, a ring gear, and a carrier. One or more of the sun gear, ring gear, and carrier can be input or output of the planetary gearset. The manner in which torque is transmitted through the clutches and gearsets determines the different gear ratios for a given transmission.
In some arrangements, however, the reverse gear ratio may be numerically too large to obtain a required reverse speed. In addition, the gear step between the first and second forward gears may be too large to permit the 1-2 and 2-1 shifts to be made with the torque converter clutch applied. Making these shifts with the torque converter clutch applied can improve transmission efficiency, fuel economy, and reduce transmission heat generation. Gear step is defined in the present disclosure as the ratio of two gear ratios.
There is a need for an automatic transmission having a gearing arrangement for automatically selecting gears and which the gearbox is configured for an available fast reverse and a close gear step 1-2 shift.